Electron discharge device



Jan. 4, 1944. Q SMYTH 2,338,306

ELECTRON DISCHARGE DEVICE Filed Sept. 11, 1941 I/VL ENTOR QRN Y PatentedJan. 4, 1944 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICEApplication September 11, 1941, Serial No. 410,351

In Great Britain August 23, 1940 5 Claims.

This invention relates to electron discharge apparatus incorporatinghigh frequency resonators of the coaxial conductor type.

In a co-pending application of J. H. Fremlin, Ser. No. 367,401, filedNovember 27, 1940, various electron discharge devices are disclosedcomprising lengths of coaxial conductor line constituting very highfrequency resonators and means for passing electron beams through thefields of the resonators for the velocity modulation of the electrons.

In such arrangements, and generally where coaxial conductor typeresonators are employed as frequency determining circuits in electrondischarge apparatus, it is desirable to provide means for tuning theresonator. Where, however, the resonator is wholly enclosed within anevacuated envelope, obvious dimculties immediately arise.

It is an object of the invention to provide a simple means, requiring nomovable parts inside the evacuated envelope, for effecting such tuningof the resonator.

According to the invention in an electron discharge device comprising -aresonator of the coaxial conductor type wholly enclosed within anevacuated envelope, adjustable tuning means is provided external to theenvelope for varying a capacity applied across an end of the resonator.

According to a further feature of the invention an electron dischargedevice comprises a quarter-wave coaxial conductor type resonator whollyenclosed within an evacuated envelope, means for producing an electronbeam traversing the field of the coaxial conductors for the velocitymodulation of electrons and an adjustable tuning device external to theenvelope adapted to apply a variable capacity across an open end of theresonator.

A preferred arrangement in accordance with the invention is illustratedin the accompanying drawing which is a sectional view of an electrondischarge device utilising the principles of velocity modulation.

Referring to the drawing, a quarter-wave type coaxial resonator R closedat one end and consisting of a tubular outer conductor A and a centralconductor B, is mounted inside an evacuated glass envelope E by means ofmica positioning members M. The conductors A and B are provided withapertures in a common diameter and fins L bounding the apertures. Acathode C and focussing electrode K are provided to project an electronbeam through the apertures to the anode P, for producing resonantoscillations in the resonator, in accordance with the principles ofoperation fully described in the copending application referred toabove. A collecting rod or probe S is sealed into the envelope oppositethe closed end of the resonator and projects into the interior thereof.

The outer conductor A is extended sufliciently far beyond the centralconductor B at the open end to prevent radiation, and the closedenvelope E is formed with a re-entrant end portion D which dips into theopen end of the tubular conductor A nearly as far as the extremity ofthe central conductor B.

A small copper disc F is mounted on one end of a threaded rod G ofinsulating material which is threaded through a fixed support H and isprovided at its other end with an adjusting knob T. The disc F can, byrotation of the knob T, be moved inside the extended portion of thetubular conductor A but still be outside the evacuated envelope and thusthrow a variable capacity across the open end of the resonator R. Itwill be seen that the movement of disc F is in a direction parallel tothe axis of the coaxial conductors.

It is appreciated that a quarter-wave oscillator of this type can onlyprovide half the output of an oscillator employing a half-wave closedresonator, and that moreover some small loss may be introduced by thepresence of the dielectric constituted by the glass wall of theenvelope. It is thought, however, that for receiving purposes thereduction in oscillator output will not be serious and that thedielectric loss can be very small if a suitable glass is used and onlysufficient capacity is added externally to give a frequency variation ofthe order of Modifications within the scope of the appended claims willoccur to those versed in the art. For example, the tuning deviceinserted into the extended end of the resonator may be a dielectric rodhaving low loss properties instead of the metal disc described above.Moreover, the external tuning device may be ganged with the means foradjusting the voltage supplies to the tube in order to maintainsynchronism between the oscillations of the electrons and the naturalfrequency of the resonator.

What is claimed is:

1. An electron discharge device including an evacuated envelope, an openended resonator having coaxial conductors, said resonator being whollywithin said envelope, oscillation generating means combined with theresonator and adjustable tuning means including a capacity elementcoaxial with and positioned at the open end movably mounted within saidreentrant portion of said envelope.

3. An electron discharge device according to claim 1 in which the outerone of said coaxial conductors has an open end and said envelope has areentrant portion extending into said open end, said external capacityelement consisting of a disc located Within said reentrant portion ofsaid envelope, and which includes adjusting means to move said disc in adirection parallel to the axis of said conductors,

4. An electron discharge device according to claim 1 in which the outerone of said coaxial conductors has an open end and said envelope has areentrant portion extending into said open end, said external capacityelement consisting of a disc located within said reentrant portion ofsaid envelope, and a rod of insulating material supporting said disc,said rod being threaded whereby rotation of the rod produces movementthereof parallel to the axis of said coaxial conductors.

5. An electron discharge device according to claim 1 in which saidcoaxial conductors constitute a resonator of the quarter wave lengthtype, said conductors having apertures therein along a common diameter,and which includes electrode means for projecting an electron beamthrough said apertures for the velocity modulation of electrons toproduce resonant oscillations in said resonator.

CHARLES NORMAN SMYTH.

